Transcript Document
Chapter 11 Reproductive Behaviors Variations in Sexual Behavior • Gender identity: how we identify sexually and what we call ourselves • Sex differences: Biological differences between males and females • Gender role: refers to the activities and dispositions that a particular society encourages for one sex or the other Gender Identity • Most people have a gender identity that matches their external appearance. • Some people have a gender identity that is opposite their biological sex. Jazz is a transgender child. See her story at: Link to Video (Extra credit opportunity) • Psychologists and researchers once believed that gender identity was learned and more a product of rearing and experience. • Current evidence strongly suggests that biological factors, especially prenatal hormones, play a large role in gender identity. Variations in Sexual Development • True hermaphrodite: someone who has both testicular and ovarian tissue—very rare • Hermaphrodites: individuals whose genitals do not match the normal development for their genetic sex • Intersex people are people are intermediate between being male or female (AKA: pseudohermaphrodite) • Video: Is It a Boy or a Girl? (1999) • Link to Video, Part One • Link to Video, Part Two • Link to Video, Part Three Sex Hormone • A chemical that is secreted by a gland, conveyed by the blood, and affects other organs Endocrine glands • Glands that produce hormones Sex Hormones Two types of sex hormones include: 1. Androgens 2. Estrogens • Both sexes have both hormones Sex and Hormones • Androgens are a groups of male sex hormones that include testosterone • Generally referred to as “male hormones” because men have higher levels than women Sex and Hormones • Estrogens include estradiol and others and are referred to as “female hormones” because women have higher levels. • Progesterone is a type of hormone that prepares the uterus for the implantation of a fertilized ovum and promotes the maintenance of pregnancy. Sexual Differentiation • Begins with the chromosomes • At six weeks of development, both sexes have primitive gonads as well as: – Mullerian ducts (precursors to female reproductive organs-- oviducts, uterus, and upper vagina) and – Wolffian ducts (precursors to male reproductive organs-vas deferens and seminal vesicles). Sexual Differentiation • The male Y chromosome includes the SRY gene which causes the primitive gonads to develop into testes, the sperm-producing organ. • The developed testes produce the hormone testosterone. • Testosterone induces the development of the penis and scrotum. • Females are not exposed to high testosterone levels and their gonads develop into ovaries, the egg-producing organs. Sex and Hormones • Sensitive periods are early periods when hormones have long-lasting effects. • Sexual differentiation depends mostly on the level of testosterone during a sensitive period. • The human sensitive period for genital formation is about the third and fourth month of pregnancy. Sex and Hormones • Sex hormones can have the following effects: 1. Organizing effects- occur mostly at sensitive stages of development. -Determine whether the brain and body will develop male or female characteristics 2. Activating effects- occur at any time of life and temporarily activate a particular response. Congenital adrenal hyperplasia (CAH) • XX female’s cortisol production leads to overstimulation of the adrenal gland. • Overstimulation of the adrenal gland leads to extra testosterone production. – The female fetus becomes partly masculinized. Congenital adrenal hyperplasia (CAH) • Research indicates that CAH girls show a greater preference for boy-typical toys than do other girls. • During adolescence and early adulthood, they also show partly masculinized interests. • Sexual interest and activity also differs for CAH girls as well. Androgen insensitivity or testicular feminization • XY male has the genital appearance of a female. • Production of androgens remains normal but they lack the androgen receptor that enables it to activate genes in a cell’s nucleus. • Condition occurs in various degrees from a smaller than average penis to genitals that develop a female appearance. Four siblings with testicular feminization syndrome (recessive sex-linked allele) 5 alpha-reductase 2 deficiency • XY males fail to produce an enzyme that converts testosterone to dihydrotestosterone. • Most look female at birth but a penis develops during adolescence and puberty. • Most then accept a male gender identity. – Brain is exposed to testosterone during early development. Biological Bases of Sexual Orientation • Research suggests that certain brain structures differ in size between heterosexual and homosexual men and women, due to the early role of sex hormones. • Sexually dimorphic nucleus (SDN): an area in the anterior hypothalamus that is larger in the male and contributes to control of male sexual behavior, (e.g., being attracted to a female). – Study of homosexual male brains found that their SDN was similar to those found in females. Biological Bases of Sexual Orientation • Twin studies suggest genetic factors. • Probability is highest in monozygotic twins and lower in dizygotic twins, and even lower in siblings and adopted brothers or sisters. • Because monozygotic twins can have opposite sexual orientations, genes are not the only factor. Biological Bases of Sexual Orientation • Sexual orientation may be influenced by testosterone levels during sensitive periods of brain development. • Male animals deprived of testosterone early in life show sexual interest in other males as adults. • Female animals exposed to testosterone during early development show an increased likelihood of mounting behavior. Biological Bases of Sexual Orientation • Laboratory research has also shown that prenatal stress can alter sexual development. • Male subjects subjected to either prenatal stress or alcohol developed male sexual behavior in addition to female sexual behaviors. • Male subjects exposed to both stress and alcohol during prenatal development had decreased sexual behavior. Biological Bases of Sexual Orientation • The probability of homosexual orientation is higher among men with older brothers. • Results suggest that a mother’s immune system may react against a protein in a son and attacks subsequent sons to alter development. [Prenatal Influences, p337]